This invention relates to a motor vehicle drive axle.
A common motor vehicle drive axle includes a center housing, a pair of axle tubes on opposite sides of the center housing, and a pair of axle bars rotatably supported on the drive axle in respective ones of the axle tubes. A gear assembly in the center housing includes a pinion gear connected to a propeller drive shaft of the motor vehicle and a differential gear set between the pinion gear and each of the axle bars. The differential gear set converts rotation of the pinion gear into rotation of the axle bars to drive respective ones of a pair of dirigible wheels on the outboard ends of the axle bars while permitting relative rotation between the axle bars when the motor vehicle turns. Heat attributable to friction in the gear assembly is transferred to liquid lubricant in a reservoir in the center housing and then to the air around the center housing through the wall of the center housing. Under severe operating conditions, e.g. towing, the heat transfer performance of the center housing may be inadequate and the temperature of the liquid lubricant may become excessive. To supplement the heat transfer performance of the center housing, it is known to adapt a ring gear of the differential gear set to push or scoop liquid lubricant from the reservoir into each of a pair of internal conduits in respective ones of the axle bars. The internal conduits transport the hot lubricant at low fluid pressure to the ends of the axle tubes where it drips onto the inside surfaces of the axle tubes. As the hot lubricant drains back to the center housing, it films or coats a relatively small fraction of the inside surfaces of the axle tubes. Since heat is transferred from the lubricant to the axle tubes through such lubricant films and since the filmed area is relatively limited, the supplemental heat transfer through the axle tubes may be inadequate to always maintain the temperature of the lubricant in a range consistent with long term durability of the gear assembly. Accordingly, manufactures continue to seek drive axles having improved heat transfer performance.
This invention is a new and improved motor vehicle drive axle including a center housing, a pair of axle tubes on opposite sides of the center housing, and a pair of axle bars rotatably supported on the drive axle in respective ones of the axle tubes. A gear assembly in the center housing includes a pinion shaft connected to a propeller drive shaft of the motor vehicle, a pinion gear on the pinion shaft, and a differential gear set between the pinion gear and each of the axle bars. A pump driven by the pinion shaft has an inlet exposed to liquid lubricant in a pool in the center housing and a discharge connected to a pair of tubular spray bars in respective ones of the axle tubes. Each spray bar has a plurality of orifices arrayed along its length constituting a corresponding plurality of nozzles aimed generally at the uppermost extremity of the inside surface of the corresponding axle tube. When the pinion shaft rotates, the pump pumps hot liquid lubricant into the spray bars at an elevated pressure and out of the spray bars through the nozzles as jets which impinge on the inside surfaces of the axle tubes near the uppermost extremities thereof. The hot liquid lubricant forms a film or coating over substantially 100% of the inside surfaces of the axle tubes as it drains back to the pool thereby to maximize the heat transfer performance of the axle tubes.